How many 'h' in 'shhh'?

Ok, this might be a completely ridiculous question, but in the case of comforting someone, how many 'h', would you put in 'shhhh...'.

Twice in my novel a character wakes up from a nightmare and is comforted by their friend/love interest and the friend is hugging them and rubbing their back and saying "shhhh..." and I can't tell how many 'h' would be an appropriate amount.